Wireless mesh communication networks typically consist of a plurality of wireless routing nodes that operate in a peer-to-peer fashion to establish communication paths to one another for the purposes of providing network access to wireless clients or mobile stations. Some wireless mesh networks are hierarchical in nature with the routing nodes that bridge wireless traffic onto a wired network at the top of the hierarchy. The wireless mesh routing nodes can be one-, two-, or multiple radio systems including omni-directional and/or directional antennas, and systems that provide backhaul traffic over the same mesh hierarchy but over multiple channels. In one-radio systems, the radio unit is used for purposes of acting as an access point to its clients, as well as acting as a backhaul to a parent routing node. In two-radio systems, one radio unit typically provides access point service to wireless clients as well as child routing nodes, while the other radio unit is used as a backhaul to a parent routing node. Multiple radio designs typically dedicate one radio for access, one or more to service the backhaul, and may also dedicate a radio for the purposes of monitoring the RF environment and other conditions on multiple radio frequencies. In certain wireless mesh networks, the backhaul radio operates in ad-hoc station mode, appearing as a peer node to the parent routing node. Those radios in the network providing access to clients operate in access point mode, providing wireless connections to mobile stations.
In wireless mesh networks operating with multiple directional antennas or over multiple channels, the routing nodes on the backhaul must coordinate the communications between the radios. One technique is to have multiple backhaul radios, one for each directional antenna and channel pair over which the radio operates. Another technique is called slotting, in which parent and child coordinate their transmissions to each other at times mutually agreed upon. A slot is the smallest unit of time during which transmissions between parent and child nodes are scheduled.
In wireless mesh networks that automatically form the network and the parent child relationships, one implementation can use discovery to determine a potential set of parents. The discovery process involves scanning channel and antenna pairs to find suitable parents. One technique is to probe, by transmitting a networking packet on the broadcast channel, which is then responded to by suitable parents. In typical wired networks or in wireless networks in which a radio is dedicated to each antenna/channel pair, the time to acquire a new parent is typically very small. An acquire packet is transmitted and the receiver is always available on the medium on which it is transmitted, be it a local area network, or on a wireless channel, directional antenna pair. However, in those instances in which a single radio supports multiple directional antennas and channels, and for which a node has no a priori knowledge of the schedule of the channel antenna pair of the potential parent node, the acquire time can be much longer.
Hierarchical wireless mesh networks inherently create certain dependencies. For example, a given routing node, and its child routing nodes, depend on the parent routing node to reach upstream destinations. Accordingly, a failure event associated with the parent node will generally cause its child nodes to seek to re-acquire another parent node. In most systems, the child nodes will generally stop servicing their own child nodes (grandchild nodes of the parent) in order to re-acquire the existing parent node, or acquire a new parent node. During this time, the grandchild nodes may also view this lack of service as a failure event and, therefore, seek to acquire a new parent node. Given that the failure occurs between the parent and child node, the overhead and delay associated with having a failure event propagate down the hierarchy are undesirable, as this condition may extend the time required for the wireless mesh to recover from the failure event at only one node.
In light of the foregoing, a need in the art exists for methods, apparatuses and systems that allow for an efficient failure recovery mechanism in wireless mesh networks. Embodiments of the present invention substantially fulfill this need.